Recently, a display device integrally comprising, for example, a liquid crystal display device (also called a display panel) and a touch-type input panel has been developed. The display device is utilized for an electronic devices (including mobile terminals such as smartphones, tablet computers, and personal assistant devices (PAD)).
One of the touch-type input panels is a handwriting input device capable of inputting data by allowing a pen or a finger to touch a display screen and allowing the pen or the finger in the touching state to move on the display screen.
The handwriting input device is also called a coordinate input device, and is constituted by providing a touch detection surface of the touch-type input panel on the display screen of the display device. Systems of the resistance type, capacitive type, electromagnetic induction type, and so on are developed as the system of sensing the handwriting input. For example, the handwriting input by pen is sensed by the touch detection surface and, this sensing data including a position of the pen on the display screen and a pressing force for pressing the display screen is converted to coordinate data and pressing force data by a touch panel (TP) controller.
The coordinate data and the pressing force data are processed by a central processing unit (CPU) such as an application processor and a microcomputer. The CPU allows movement locus of the pen to be stored in a frame memory as video data, which may also be called drawing data, and transmits the video data to the liquid crystal display device, which is configured to display the data, at a frame rate of, for example, approximately 60 Hz. Thus, The movement locus by pen is displayed on a display module of a liquid crystal display device as a line and updated.
In the above-described devices, processing delay caused by executing programs such as an operation system (OS) and applications operated on the CPU, or delay associated with interfaces between the CPU and a TP controller IC or LCD controller occurs.
As a result, it is difficult for the above devices to make the line drawn on the display device follow a touch position (pen tip) instructed by a user immediately at the handwriting input mode.
The delay is, generally, approximately 100 ms, which is considered as a reason for degrading convenience of the handwriting input device. In addition, there is another problem that during the handwriting input, the power consumption becomes increased since the display screen needs to continue updated as a whole, at any time, at a frame rate of, for example, approximately 60 Hz.